// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef BASE_MESSAGE_LOOP_MESSAGE_PUMP_LIBEVENT_H_
#define BASE_MESSAGE_LOOP_MESSAGE_PUMP_LIBEVENT_H_

#include "base/compiler_specific.h"
#include "base/macros.h"
#include "base/message_loop/message_pump.h"
#include "base/threading/thread_checker.h"
#include "base/time/time.h"

// Declare structs we need from libevent.h rather than including it
struct event_base;
struct event;

namespace base {

// Class to monitor sockets and issue callbacks when sockets are ready for I/O
// TODO(dkegel): add support for background file IO somehow
class BASE_EXPORT MessagePumpLibevent : public MessagePump {
public:
    // Used with WatchFileDescriptor to asynchronously monitor the I/O readiness
    // of a file descriptor.
    class Watcher {
    public:
        // Called from MessageLoop::Run when an FD can be read from/written to
        // without blocking
        virtual void OnFileCanReadWithoutBlocking(int fd) = 0;
        virtual void OnFileCanWriteWithoutBlocking(int fd) = 0;

    protected:
        virtual ~Watcher() { }
    };

    // Object returned by WatchFileDescriptor to manage further watching.
    class FileDescriptorWatcher {
    public:
        FileDescriptorWatcher();
        ~FileDescriptorWatcher(); // Implicitly calls StopWatchingFileDescriptor.

        // NOTE: These methods aren't called StartWatching()/StopWatching() to
        // avoid confusion with the win32 ObjectWatcher class.

        // Stop watching the FD, always safe to call.  No-op if there's nothing
        // to do.
        bool StopWatchingFileDescriptor();

    private:
        friend class MessagePumpLibevent;
        friend class MessagePumpLibeventTest;

        // Called by MessagePumpLibevent, ownership of |e| is transferred to this
        // object.
        void Init(event* e);

        // Used by MessagePumpLibevent to take ownership of event_.
        event* ReleaseEvent();

        void set_pump(MessagePumpLibevent* pump) { pump_ = pump; }
        MessagePumpLibevent* pump() const { return pump_; }

        void set_watcher(Watcher* watcher) { watcher_ = watcher; }

        void OnFileCanReadWithoutBlocking(int fd, MessagePumpLibevent* pump);
        void OnFileCanWriteWithoutBlocking(int fd, MessagePumpLibevent* pump);

        event* event_;
        MessagePumpLibevent* pump_;
        Watcher* watcher_;
        // If this pointer is non-NULL, the pointee is set to true in the
        // destructor.
        bool* was_destroyed_;

        DISALLOW_COPY_AND_ASSIGN(FileDescriptorWatcher);
    };

    enum Mode {
        WATCH_READ = 1 << 0,
        WATCH_WRITE = 1 << 1,
        WATCH_READ_WRITE = WATCH_READ | WATCH_WRITE
    };

    MessagePumpLibevent();
    ~MessagePumpLibevent() override;

    // Have the current thread's message loop watch for a a situation in which
    // reading/writing to the FD can be performed without blocking.
    // Callers must provide a preallocated FileDescriptorWatcher object which
    // can later be used to manage the lifetime of this event.
    // If a FileDescriptorWatcher is passed in which is already attached to
    // an event, then the effect is cumulative i.e. after the call |controller|
    // will watch both the previous event and the new one.
    // If an error occurs while calling this method in a cumulative fashion, the
    // event previously attached to |controller| is aborted.
    // Returns true on success.
    // Must be called on the same thread the message_pump is running on.
    // TODO(dkegel): switch to edge-triggered readiness notification
    bool WatchFileDescriptor(int fd,
        bool persistent,
        int mode,
        FileDescriptorWatcher* controller,
        Watcher* delegate);

    // MessagePump methods:
    void Run(Delegate* delegate) override;
    void Quit() override;
    void ScheduleWork() override;
    void ScheduleDelayedWork(const TimeTicks& delayed_work_time) override;

private:
    friend class MessagePumpLibeventTest;

    void WillProcessIOEvent();
    void DidProcessIOEvent();

    // Risky part of constructor.  Returns true on success.
    bool Init();

    // Called by libevent to tell us a registered FD can be read/written to.
    static void OnLibeventNotification(int fd, short flags,
        void* context);

    // Unix pipe used to implement ScheduleWork()
    // ... callback; called by libevent inside Run() when pipe is ready to read
    static void OnWakeup(int socket, short flags, void* context);

    // This flag is set to false when Run should return.
    bool keep_running_;

    // This flag is set when inside Run.
    bool in_run_;

    // This flag is set if libevent has processed I/O events.
    bool processed_io_events_;

    // The time at which we should call DoDelayedWork.
    TimeTicks delayed_work_time_;

    // Libevent dispatcher.  Watches all sockets registered with it, and sends
    // readiness callbacks when a socket is ready for I/O.
    event_base* event_base_;

    // ... write end; ScheduleWork() writes a single byte to it
    int wakeup_pipe_in_;
    // ... read end; OnWakeup reads it and then breaks Run() out of its sleep
    int wakeup_pipe_out_;
    // ... libevent wrapper for read end
    event* wakeup_event_;

    ThreadChecker watch_file_descriptor_caller_checker_;
    DISALLOW_COPY_AND_ASSIGN(MessagePumpLibevent);
};

} // namespace base

#endif // BASE_MESSAGE_LOOP_MESSAGE_PUMP_LIBEVENT_H_
